1. FIELD OF THE INVENTION
This invention relates to the field of joinery and systems for joining component parts together. More particularly this invention relates to timber joinery and joints which are effective to join various beams to posts, purlins to rafters and other components to be joined which are encountered during construction procedures such as stair treads and risers to stringers, the joints not being visible.
2. DESCRIPTION OF THE PRIOR ART
The rising cost of labor and materials have made building construction and especially the construction of homes increasingly more expensive. In addition the cost of heating and cooling a building has increased many times over in recent years. In order to keep the costs of construction, heat, cooling and maintenance within reasonable limits and therefore affordable to the general public, innovations have been necessary. In part because of the availability of prefabricated structure-wall and curtain-wall panels, there has been a return to the post and beam type of modular construction which lends itself to a prefabrication of the many construction components away from the construction site. By prefabrication and precutting many of the components of the structure at a manufacturing facility, many procedures may be used to improve the fabrication efficiency and improve the quality of the components as well as reduce the construction time.
Many types of joints have been and are currently being used by builders who are building post and beam types of structures. There are joints called ANCHOR-BEAM; KNEE-BRACE; SCARF; TUSK TENON; CORNER JOINTS; TONGUE AND FORK; COLLAR-TIE; to name but a few. However, perhaps the most basic timber-framing joint is the MORTISE and TENON. It would be desireable, because of the simplicity of the joint, to be able to use it for many of the joining applications. However, the joint should be designed to carry only a light load. Adding a shoulder to the mortise and tenon gives it an entirely different load-bearing quality. Other simple and useful joints are the DOVETAIL and the HOUSED-DOVETAIL JOINTS which adversly effect the strength of the beam because the top chord portion of the mortised beam is violated. The simple dovetail is commonly used to join the smaller members, such as joists and purlins and is designed to carry loads. The housed-dovetail is unique in that it is the only major timber connection that does not use a peg. The joint is designed so that the timber can be placed in the structure after the "bents" have been raised. That is to say that the female portion or the "mortise" portion does not have to be moved away in order to make the connection to the beam. The wedging effect of the dovetail and the weight of the beam itself lock the joint in place. The "housing" helps the timber retain its strength at the connection. The dovetail joint is designed to have a taper in a single plane with a resulting limited rigidity. The TUSK TENON JOINT is stronger, in part, because it does not violate the structure of the mortised member and it can be used in place of the housed-dovetail except that it must be pegged through the tenon in order to hold the joint together.
Many of the joints and methods of timber joinery are clearly explained in the book, Building The Timber Frame House The Revival of A Forgotten Craft, Tedd Benson and James Gruber, Published by Charles Scribner's Sons. The various joints are illustrated on pages 40-50.
A dual tapered dovetail shaped mortise and tenon joint is disclosed in U.S. Pat. No. 4,019,298 by Johnson. The joint is described as a dual tapered dovetail shaped mortise formed within a joist to receive a dual tapered dovetail shaped tenon extending from a beam. Laterally oriented cavities are disposed within opposite faces of the mortise to receive correspondingly configured ridges formed integral with the mating tenon. The resulting frictional interlock between the mortise and the tenon created by two forces acting in opposition to one another rigidly secures the beam to the joist without play therebetween. It should be further noted that the outer surface of the dual tapered tenon is non-parallel to the end surface of the beam integral with the tapered tenon, whereby the thickness of the tenon diminishes in the downward direction. Thus the tenon is tapered in two planes, which planes are normal to one another. The length of the tenon is the same as the vertical dimension of the beam integral with the tenon.
In U.S. Pat. No. 4,492,489, Mortice and Tenon Joint there is disclosed a mortice and tenon joint of two structural members which avoids the protrusion of the tenon beyond the mortice. Across the tenon of one member there is cut a dovetail aperture or slot and a movable tapering wedge of similar dovetail cross-section is slidably housed within a tapering channel also of similar dovetail cross-section which crosses the mortice of the other member such that when the tenon is inserted wholly into the mortice the wedge may be driven along the tapered channel to become firmly engaged within the dovetail aperture or slot thus to lock the members together and prevent them from separating until the wedge is withdrawn.
Further examples of prior art use of the dovetail shaped mortise and tenon joint may be found in U.S. Pat. Nos. 3,090,086, directed to the cabinet making art; 3,683,429, illustrating cross frame members secured to the side-frame members of a bed frame; 2,793,407 and 4,643,607, teaching the use of dovetail joints in furniture; and 2,392,551, 3,148,477, 3,396,499, 3,410,044, 3,562,988, and 3,664,011, disclosing the aligning of structural members of means of dovetail joints.